Preparation Of Test Specimens Research Articles

Methods to Obtain Weld Discontinuities in Spot-Welded Joints Made of Advanced High-Strength Steels

Resistance spot welding is the major joining technique in mass car production. This applies in particular to high-strength steel and advanced high-strength steel (AHSS) joining of thin sheet steel components for lightweight body shell structures. Joining of AHSS in mass production might lead to weld discontinuities under certain circumstances. Those discontinuities in form of cracks might be an initial start of cracking in the spot-welded joints regarding fatigue loads. It is of great interest to figure out, if, in comparison to specimens without weld discontinuities, the crack initiating point changes and if the fatigue resistance might be reduced by the discontinuities. In this contribution, an overview of potential discontinuities is given. Their possible causes are discussed and means for their detection are highlighted. Among the possible causes of weld discontinuities, two major groups are distinguished: the welding parameters as primary influences in the welding process, and the production-specific influences as secondary ones. With emphasis on major cracks penetrating the weld nugget, these influences are analysed. Finally, a combination of extreme welding parameters with production-specific influences is chosen in order to establish a method which enables the preparation of fatigue test specimens with reproducible major cracks in different locations of the spot-welded joints. This method is then applied in order to prepare spot weld specimens for fatigue tests.

An internal variable approach of orientation dependent deformation mechanism of rolled AZ31 magnesium alloy

Load relaxation behavior of an AZ31 Mg alloy has been studied in relation to temperature and orientation dependence. The rolled plate with 50 mm thickness was first homogenized at 400 °C for 4 h before preparing test specimens in the directions of 0° (RD), 45°, and 90° (ND) from the rolling direction. A series of tensile tests was consequently carried out under a strain rate of 10−2/s at room temperature (RT), 100 °C, and 200 °C. The RD specimens were found to deform mainly by dislocation slips without twinning. The 45° and 90° specimens were, on the other hand, found to deform in a combined mode of twinning and dislocation slips. Load relaxation tests were also performed to obtain flow curves in terms of stress and strain rate at the three different temperatures. The flow curves in terms of stress vs. strain rate were also found to consist of a plasticity curve due to dislocation glides in the lower strain rate region and a twin curve in the high strain rate range for the 45° and 90° specimens as prescribed by an internal variable theory. These results were consistent with the tensile test results and were further confirmed by microstructure observations.

Deformation mechanism temperature-dependence of AZ31 magnesium alloy

The deformation behavior of AZ31 Mg alloy is studied here in relation to the temperature. A rolled plate with a thickness of 50 mm was first homogenized at 400 °C for 4 h before preparing test specimens with the tensile axis parallel to the rolling direction (RD). A series of tensile tests was then carried out at a strain rate of 10−2/s together with load relaxation tests to obtain flow curves in terms of the stress and strain rate at room temperature (RT), 100 °C, 200 °C, and 300 °C. The flow curves were found to represent the usual grain matrix deformation (GMD) behavior, consisting of the accumulation and relaxation of glide dislocations at temperatures of less than 100 °C. At temperatures greater than 200 °C, grain boundary sliding (GBS) was found to play an important role, as described in theories related to an internal variable. The GBS could be characterized as a non-Newtonian viscous flow with a power index value of M g = 0.5.

Comparison of test specimen preparation techniques for pervious concrete pavements

The objective of this study was to evaluate different pervious concrete test specimen preparation techniques in an effort to produce specimens having properties similar to in-place pervious concrete pavement. Cylinders and slabs were cast using pervious concrete from three different paving projects using different procedures. The comparisons of cast specimens to pavement cores were based on infiltration rate, density, and porosity. Of the cylinder consolidation procedures tested, the standard Proctor hammer provided the least variability of results and yielded properties similar to the in-place pavement. However, 600 mm square slabs were even more consistent with the in-place pavement density and porosity.

Laboratory Apparatus and Procedures for Preparing Test Specimens of Slurry Mixed Soils

Abstract A laboratory mixing apparatus used to prepare test specimens of columns of soil mixed with slurries consisting of clay, typically bentonite, and granular zero-valent iron (ZVI) is described. The slurries are injected and simultaneously mixed into the soil via a hollow-stem auger to mimic the process that occurs in the field associated with the remediation of source zones contaminated with chlorinated solvents (e.g., carbon tetrachloride and trichloroethylene) using large-diameter (e.g., 2.4 m or 8 ft) hollow-stem augers. The presentation includes descriptions of the testing apparatus and procedures for preparing the test columns, mixing the slurries into the base (host) soil, and determining the resulting vertical distributions in the physical properties (e.g., unit weight, water content, porosity, void ratio, clay content, ZVI content, and degree of saturation) of the post-mixed column specimens. Example results of the vertical distributions in physical properties as well as of treatability studies for base soils that were contaminated with chlorinated solvents are provided to illustrate the use of the laboratory apparatus and testing procedures.

The Effect of Component Alignment on Proximal Femoral Strength with the Birmingham Mid-Head Resection

The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem femoral prosthesis designed for patients with compromised femoral head anatomy unsuitable for a traditional hip resurfacing arthroplasty. Similar to hip resurfacing, the BMHR preserves the femoral neck, however, it is not known if the femoral neck fracture risks associated with hip resurfacing pose the same risk to a mid-head resection arthroplasty. The current study examined the effect of coronal alignment on proximal femoral strength with the BMHR. Sixteen pairs of fresh-frozen cadaveric femurs were divided into 2 equal alignment groups. Individual pairs were divided into a control and a test specimen. A power analysis revealed 8 pairs each would be needed to detect an effect size of approximately 500 N (α = 0.05; β = 1-0.8; population SD 500 N). The first alignment group prepared test specimens in 10° of relative valgus alignment, while the second group prepared test femurs in 10° of relative varus. All control specimens were prepared with the implant aligned with the native neck-shaft angle of the femur. Femurs were tested in axial compression in single-leg stance. There was no significant difference between matched paired femurs prepared in varus alignment (mean 4324 N; SD 2207) compared to controls (mean 4114; SD 2153; P = .996). Likewise, there was no difference between femurs prepared in valgus alignment (mean 4623; SD 1608) and matched paired control specimens (mean 4761; SD 1290; P = .999). There was also no difference between control groups (P = .897). Femurs were well matched for BMD and anatomic parameters. The findings of the current study are in contrast to previous studies investigating implant alignment in hip resurfacing. A valgus aligned implant did not appear to strengthen, nor a varus implant weaken, proximal femoral strength compared to a neutrally aligned implant. Failure of the proximal femur implanted with a BMHR appears less sensitive to variations in implant alignment than a typical hip resurfacing.

Unfired clay masonry bricks incorporating slate waste

This paper discusses the potential of using slate waste generated from roofing slate production in the UK in the manufacture of unfired clay masonry bricks. Ground granulated blast-furnace slag activated by lime and Portland cement were used to stabilise Lower Oxford Clay incorporating slate waste in the preparation of laboratory cylindrical test specimens. The specimens were moist cured at room temperature (20±2°C) for between 3 and 90 days before testing for compressive strength. The drying and linear expansion behaviours of the test samples were assessed by means of moisture content measurement (at the age of testing) and linear expansion measurement after soaking the samples in deionised water. The strength of the cement-activated blended mixture was lower than that of the lime-activated mixtures. An environmental comparison of the unfired clay masonry bricks with mainstream construction (fired) bricks shows that the unfired clay bricks have good environmental characteristics over a range of important criteria. These results suggest that there is potential for using activated slag mixtures in the manufacture of bricks for low-cost environmentally friendly housing and energy-efficient masonry wall construction within the UK.

Suitability of auger drill sampling for the measurement of moisture content gradient in kiln-dried South African grown Eucalyptus grandis poles

Moisture content (MC) gradient at the time of preservation plays a pivotal role in determining the success of the preservation process. The South African pole drying industry relies on auger drill sampling to determine whether the MC of dried poles is acceptable for preservative treatment. The objectives of this study were to determine: (i) the reliability and (ii) potential sources of errors of the auger drill MC sampling method on kiln dried E. grandis poles. Destructive oven-dry MC determination on sample blocks of 12.5 mm thickness and 25 mm width as the benchmark method and auger drill samples in increments of 25 mm were used to determine the MC gradient at the theoretical ground line (TGL) of poles. Results showed that the MC of 25 mm deep increment auger drill samples did not differ from those measured using the block method. However, there were differences between MC values measured using the auger drill and block methods when samples of 50 mm or 75 mm in length were considered. Differences in MC values measured after drying also occurred in parts of the poles where moisture was still high, i.e., above fibre saturation point. It was concluded that SANS 5983 (South African Bureau of Standards. Standard method for preparation of test specimens for moisture content determination in timber and timber products, 2008), which specifies taking single radial auger drill samples of depth 70±5 mm at mid length, is a reliable method for measuring MC in a kiln dried E. grandis pole. It is recommended that MC is determined in auger increments of 25 mm at the most critical zone of a pole, such as the TGL rather than mid length.

The Effect of Flash Freezing on Variability in Spinal Cord Compression Behavior

The compression behavior of spinal cord tissue is important for understanding spinal cord injury mechanics but has not yet been established. Characterizing compression behavior assumes precise specimen geometry; however, preparing test specimens of spinal cord tissue is complicated by the extreme compliance of the tissue. The objectives of this study were to determine the effect of flash freezing on both specimen preparation and mechanical response and to quantify the effect of small deviations in specimen geometry on mechanical behavior. Specimens of porcine spinal cord white matter were harvested immediately following sacrifice. The tissue was divided into two groups: partially frozen specimens were flash frozen (60 s at -80 degrees C) prior to cutting, while fresh specimens were kept at room temperature. Specimens were tested in unconfined compression at strain rates of 0.05 s(-1) and 5.0 s(-1) to 40% strain. Parametric finite element analyses were used to investigate the effect of specimen face angle, cross section, and interface friction on the mechanical response. Flash freezing did not affect the mean mechanical behavior of the tissue but did reduce the variability in the response across specimens (p<0.05). Freezing also reduced variability in the specimen geometry. Variations in specimen face angle (0-10 deg) resulted in a 34% coefficient of variation and a 60% underestimation of peak stress. The effect of geometry on variation and error was greater than that of interface friction. Taken together, these findings demonstrate the advantages of flash freezing in biomechanical studies of spine cord tissue.

An Experimental Study of Water Vapor Pressure Change by Ambient Temperature at the Interface between Concrete and Fluid-Applied Membrane Layer

Over about 30% of problems in construction is related to water-leaking, and the loss from this problem can incur as much as three times the cost of initial construction. Thus, water vapor pressure is known to be the primary cause of defective waterproofing. Accordingly, the theories on the relationship between water pressure and temperature as well as damp-proofing volume of concrete and the change in vapor pressure volume were reviewed and analyzed in this study by making test samples after spraying a dampness remover and applying waterproofing materials to the prepared test specimens. The result of measuring water vapor pressure with the surface temperature of the waterproofing (fluid-applied membrane) layer at the experimental temperature setting of about 10℃, which is the annual average temperature of Seoul, indicated that (1) the temperature of the fluid-applied membrane elevated to about 40℃, and the water vapor pressure generated from the fluid-applied membrane was about 0.03 N/㎟ when the surface temperature of the waterproofing layer was raised to about 80℃. (2) when the temperature of the fluid-applied membrane of the waterproofing layer was raised from 30℃ to 35℃, water vapor pressure of about 0.01 N/mm2was generated, and (3) when a thermal source was applied to the fluid-applied membrane (waterproofing) layer, the temperature increased from 35℃ to 40℃, and approximately 0.005 N/㎟ of water vapor pressure was generated.

Effect of machining parameters on high-cycle fatigue behaviour of aluminium matrix composites reinforced with silicon carbide particulates

The proposed paper aims to investigate the impact of the machining conditions on the machinability and fatigue variance of aluminium matrix composite reinforced with silicon carbide particulates (SiC p). An experimental approach using three machining speeds and two feed rates has been conducted for preparing test specimens. Firstly, the surface quality of machined specimen is studied through different roughness inspections which lead to display clearness the influence of machining parameters on the finished surfaces. Secondly, the morphology of uncoated tungsten carbide tools used for turning operations is discussed. Then, tensile test is conducted in order to describe how material behaves and to determine yield stress value under which fatigue stresses would be chosen for tests. Finally, the fatigue tests were carried out on cut specimens and fatigue life for the considered composite is studied under two stress amplitudes, using 4-point reversed bending loads. Different experiments have been performed at room temperature up to failure in order to investigate the behaviour of material in each case of chosen domain. Particularly, the behaviour of composites under stress-controlled conditions has been discussed.

CENTRIFUGALLY MANUFACTURED HOLLOW CONCRETE‐FILLED STEEL TUBULAR COLUMNS

Hollow concrete‐filled steel tubular elements (H‐CFSTs) represent a type of composite steel‐concrete elements. These elements are usually produced by spinning. During this process wet concrete mix in the steel tube is displaced and compacted by centrifugal force and the concrete core so formed achieves better physical and mechanical properties in comparison with other compaction methods. These improvements are related to concrete density, Young's modulus, Poisson’ s ratio, compressive strength, deformability as well as to a more uniform distribution of fine and coarse aggregates and binding particles along the thickness of the hollow concrete core formed by multi‐layering centrifugation process. The peculiarities of the spinning process, recommendations for proportioning the components for the specimens manufacture, spinning time needed for displacement and compaction of concrete mix, preparation of specimens for testing and testing methods used are presented in this paper.

Validation of an alkali reaction, borate fusion, X-ray fluorescence method for silicon metal

The value assignment of candidate Standard Reference Material (SRM®) 57b Silicon Metal provided an opportunity to develop an alkali reaction procedure as a precursor to borate fusion for the preparation of test specimens from the metal powder for X-ray fluorescence spectrometry (XRF). Suggested for this purpose by Blanchette in a 2002 Advances in X-ray Analysis article [45, 415–420 (2002)], the alkali reaction uses LiOH∙H2O to convert Si to Li2SiO3. Lithium silicate is fused with lithium borate flux without damage to platinum ware. Once specimens are fused and cast as beads, calibration standards are prepared to closely match the compositions of the specimens, allowing a linear calibration for each analyte. The XRF method yields results that are directly traceable to the mole through NIST SRM spectrometric solutions. The method was validated in two ways. First, the reaction was used on older SRMs for Si metal: SRM 57 and SRM 57a. Second, XRF results for candidate SRM 57b were compared to results obtained using prompt gamma-ray activation analysis (PGAA) and inductively coupled plasma optical emission spectrometry (ICPOES). Bias tests show the XRF results are accurate for the elements Al, S, Ca, Ti, Cr, Mn, Ni, Cu, and Zr. Levels of S, Ca, Cr, and Cu in candidate SRM 57b are near the limits of quantification of the borate fusion method. Iron results may be subject to a low bias. Phosphorus is not quantitatively retained during the alkali reaction and borate fusion. These elements, plus B, which cannot be determined after borate fusion, are listed in manufacturing specifications for Si metal.

Improvement of carbon fiber surface properties using electron beam irradiation

Carbon fiber-reinforced advance composites have been used for structural applications, mainly on account of their mechanical properties. The main factor for a good mechanical performance of carbon fiber-reinforced composite is the interfacial interaction between its components, which are carbon fiber and polymeric matrix. The aim of this study is to improve the surface properties of the carbon fiber using ionizing radiation from an electron beam to obtain better adhesion properties in the resultant composite. EB radiation was applied on the carbon fiber itself before preparing test specimens for the mechanical tests. Experimental results showed that EB irradiation improved the tensile strength of carbon fiber samples. The maximum value in tensile strength was reached using doses of about 250 kGy. After breakage, the morphology aspect of the tensile specimens prepared with irradiated and non-irradiated carbon fibers were evaluated. SEM micrographs showed modifications on the carbon fiber surface.

Interlaboratory Comparison of the Thickness of the Destroyed Surface Layer of Closed-Cell Foam Insulation Specimens

Abstract The preparation of closed-cell foam insulation test specimens can affect the results of a number of hygrothermal property measurements. In particular, the thickness of the destroyed surface layer affects the measurement of gas diffusion coefficients and thermal conductivity. Multiple specimen preparation methods are in use, as well as multiple methods to measure the thickness of the destroyed surface layer. A ruggedness test, including an interlaboratory comparison, was conducted by an ASTM technical committee to examine the variations due to both of these factors. The results are important in understanding the likely range in values for each preparation technique. The results also demonstrate a sensitivity to the measurement technique.

New Sample Holder for the Preparation of Undisturbed Fine-Grained Soil Specimens for Laboratory Element Testing

Abstract The paper describes a new soil sample holding device, the undisturbed soil sample holder (USSH), which has the ability to minimize potential sample disturbance during the preparation of relatively soft fine-grained cylindrical soil specimens. The USSH is capable of providing suitable external, uniform lateral confinement to a sample of soil extruded from a field sampling tube. The device comprises a split hollow cylindrical aluminum housing that is internally lined with a flexible synthetic foam material. The foam lining allows the diameter of the cylindrical cavity of the USSH to be variable, while maintaining the shape of the cavity cylindrical. The device has the ability to essentially eliminate the sample freestanding period that is commonly associated with conventional preparation methods and to reduce potentially significant soil deformations that occur due to the self-weight of the sample. The effectiveness of the USSH in minimizing sample disturbance is demonstrated using comparative laboratory tests conducted on relatively soft soil specimens prepared with and without the USSH. The observed axial strains during specimen preparation, volumetric strains during consolidation, and stress-strain-pore water pressure response during undrained triaxial shear testing show that the USSH contributes to the preparation of undisturbed soil specimens for element testing.

Oil resistance and physical properties of in situ epoxidized natural rubber from high ammonia concentrated latex

AbstractEpoxidized natural rubber (ENR) was prepared via in situ epoxidation from high ammonia concentrated natural rubber latex with formic acid and hydrogen peroxide in the presence of a surfactant at 50°C for 4, 8, and 12 h. The obtained ENRs containing 20, 45, and 65 mol % of expoxide groups were denoted ENR20, ENR45, and ENR65, respectively. The differential scanning calorimetric study revealed that they exhibited higher glass transition temperatures than that of natural rubber (−62.4°C), at −38.2°C for ENR20, −27.8°C for ENR45, and −19.7°C for ENR 65. It was clearly seen that their glass transition temperatures increased as the amount of epoxide groups increased. The prepared ENRs were compounded and vulcanized to prepare test specimens for determination of oil resistance and various physical properties. It was found that the swelling of ENRs in oils was substantially less than that of natural rubber. The oil resistance of ENR65 was comparable to that of nitrile rubber, commonly used as oil resistant rubber. ENR65 also showed higher hardness than other ENRs. Contrarily, ENR20 possessed superior tensile strength and compression set when compared with other ENRs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3948–3955, 2006

A system for studying the effect of mechanical stress on the elongation behavior of immobilized plant cells

The ability to apply controllable mechanical compressive force is essential for the study of plant cells responses to environmental stimulations. The work presented here aims towards establishing a system, which consists of a fabricated apparatus (including a loading unit, displacement sensor, data collector and processor, and a feedback control) and a protocol for test specimen preparation and force loading. By using a force–feedback control circuit coupled to a microchip, delivering the pre-defined and actual controlled stimulus is achieved. To calibrate the apparatus, the corresponding voltages are compared to the known weights. A linear regression is fit to the experimental data and a standardized coefficient of 0.998 is calculated. The morphological changes in response to mechanical stresses were investigated in agarose gel embedded chrysanthemum protoplasts, which tended to be elongated with a preferential axis oriented perpendicularly to the compressive stress direction. The results also indicated that there existed a certain dose-dependent relationship between the intensity of compressive force and the stress-induced responses. Additionally, the elongation response with preferential orientation was inhibited by application of RGD peptides, and its inverted sequence, DGR peptides failed to antagonize the effect of mechanical force on elongation performance.

Transitioning from Texas Gyratory Compactor to Superpave Gyratory Compactor

The Strategic Highway Research Program expended great effort in developing the Superpave® gyratory compactor (SGC) as a modern, technologically advanced tool for the design of hot-mix asphalt (HMA) paving mixtures and for preparation of realistic test specimens for laboratory evaluation. Since the widely accepted SGC was designed to produce specimens similar to actual pavement layers and since the current series of Texas Department of Transportation (TxDOT) HMA paving mixtures have demonstrated acceptable performance, TxDOT wished to replace the Texas gyratory compactor (TGC) with the SGC for the design of its current repertoire of dense-graded mixtures. In the first phase of this study, the authors developed a specification for the number of design gyrations with the SGC to achieve the same optimum asphalt content (OAC) as that obtained with the TGC. However, on the basis of past experience, review of the literature, and feedback from TxDOT, the design OAC was considered to be too low; mixtures that may be susceptible to fatigue cracking resulted. To mitigate this problem, the authors revised the specification for use of the SGC so that the resulting mixtures had an increased OAC. This revision was done by comparing the rutting resistance of HMA mixtures designed at different numbers of gyrations with the Hamburg wheel-tracking device and then selecting the lowest number of gyrations that did not compromise rutting resistance of the mixture. Results show that it is possible to select a considerably lower number of design gyrations with the SGC without a significant decrease in rutting performance of the mixtures.

Transitioning from Texas Gyratory Compactor to Superpave Gyratory Compactor

The Strategic Highway Research Program expended great effort in developing the Superpave® gyratory compactor (SGC) as a modern, technologically advanced tool for the design of hot-mix asphalt (HMA) paving mixtures and for preparation of realistic test specimens for laboratory evaluation. Since the widely accepted SGC was designed to produce specimens similar to actual pavement layers and since the current series of Texas Department of Transportation (TxDOT) HMA paving mixtures have demonstrated acceptable performance, TxDOT wished to replace the Texas gyratory compactor (TGC) with the SGC for the design of its current repertoire of dense-graded mixtures. In the first phase of this study, the authors developed a specification for the number of design gyrations with the SGC to achieve the same optimum asphalt content (OAC) as that obtained with the TGC. However, on the basis of past experience, review of the literature, and feedback from TxDOT, the design OAC was considered to be too low; mixtures that may be susceptible to fatigue cracking resulted. To mitigate this problem, the authors revised the specification for use of the SGC so that the resulting mixtures had an increased OAC. This revision was done by comparing the rutting resistance of HMA mixtures designed at different numbers of gyrations with the Hamburg wheel-tracking device and then selecting the lowest number of gyrations that did not compromise rutting resistance of the mixture. Results show that it is possible to select a considerably lower number of design gyrations with the SGC without a significant decrease in rutting performance of the mixtures.